[3.0] direct3d11: fix leak when using NVIDIA Super Resolution V2

Merged Steve Lhomme requested to merge robUx4/vlc:30-super-leaks/4 into 3.0.x

Rather than forcing the filling of a whole texture and then place it, as in !3664 (closed), we convert to RGBA when doing the upscaling. This also avoids the leak and it keeps the SPU positioning/stretching correct.

There's also an extra fix for sources with a non 1:1 SAR (as some DVDs).

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